Drilling tool

ABSTRACT

A drilling tool for machine tools includes a drill shank provided with a radially outwardly projecting feed helix. The drilling tool also includes a drilling head disposed at the end of the drill shank and having two segment sections which are delimited radially outwardly by partially cylindrical peripheral surfaces and separated from each other by axially parallel chip grooves which are adjacent in the peripheral direction. The drilling head also includes at least two cutting plates disposed at different radial spacings from a drilling tool axis and each having a cutting edge projecting beyond the drilling head. The chip grooves are delimited on the side of the cutting plates by at least one axially parallel radial chip-deflection surface and by a chip-guide surface disposed on the adjacent segment section. The chip-deflection surfaces terminate at an axial spacing from the cutting edges at a substantially radial rear free edge and merge there into a chip-feed surface which delimits the relevant segment section at the rear in the direction of the drill shank, rising helically to the following chip channel. The annular space between the chip-feed surface and the end of the feed helix at the drilling head end forms a chip-stowing space from which the chips produced during drilling are carried away by the helix.

FIELD OF THE INVENTION

The invention is related to a drilling tool for machine tools,especially for machining metal or plastic workpieces.

BACKGROUND OF THE INVENTION

A drilling tool of this type is known (DE-A-42 14 528), which is adaptedto be clamped in a machine spindle and comprises a drill shank providedwith a feed helix delimiting a chip removal groove and a drill headdisposed on the face of the drill shank. The drill head has two segmentportions which are delimited radially outwardly by partially cylindricalcircumferential surfaces which together form a common circumferentialcylinder and which are separated from each other by chip channels whichadjoin each other in a circumferential direction, which are alignedessentially axially parallel, and which merge in the chip removal groovein the chip flow direction. The drill head further has at least twocutting inserts which are disposed at different radial distances fromthe axis of the drill with partially overlapping working areas in anappertaining recess of the segment portions in the region of an axiallyparallel radial chip diverting surface, preferably with the face alignedthereto, and which have at least one active cutting edge protruding overthe face of the drill head, wherein the cutting edge of the outermostcutting insert protrudes radially over the appertaining partiallycylindrical circumferential surface and wherein the drill head has alarger outer diameter than the drill shank. By a specific alignment ofthe cutting inserts which partially overlap in the effective region oftheir cutting edges it is ensured that the lateral forces acting on thecutting edges during the drilling operation are essentially compensated,so that workpieces can be bored essentially without guide means. Thecentering is effected by means of an axially centered centering drill.The chip grooves which extend axially parallel along the drill shank andwhich have a triangular cross section each merge in the direction ofchip flow in a relatively steep helical chip transport groove providedin the drill shank, which grooves are formed into the material of theshank. The edges of the chip removal grooves are delimited by a feedhelix which serves on the one hand to guide the drill within the borehole and on the other hand to delimited the chip removal grooves. Aseparate chip removal groove is assigned to each chip channel in thedrill shank, into which groove the channel merges in the direction ofchip flow. In this design the chips are especially pushed outwardsthrough the chip removal grooves under the influence of a coolant. Bythe forming of the comparatively broad feed helix, it is attempted toprevent chips from being distributed out of the chip removal groovesover the circumference of the drill shank, which would otherwise bearthe danger of the chips fusing with the bore wall and the drill shank,thus leading to a destruction of the bore and the drilling tool. Afurther problem exists in that the chip channel forms, in the region ofthe inner insert, a comparatively broad chip space having a triangularcross section, which chip space tightens toward the rear in thedirection of chip flow in a funnel-like manner. This leads to the resultthat the chip may be formed to be relatively broad during its creationand then has to be forced into the chip removal groove with deformationwork. By this a large amount of the thrust energy imparted to the chipsin their creation is lost in the form of deformation work and cannot beused to aid the removal of the chips. Furthermore, the deformationforces are partially transformed into lateral forces which cause aradial deflection of the drill head and therefore a degradation of thedrilling efficiency and quality. For this reason guideless drills ofthis type can be employed only for comparatively shallow bores up to adepth of up to 6×D, wherein D denotes the diameter of the bore.

Based on this it is the object of the invention to develop a drillingtool which may be used for great bore depths of 12×d and more, and whichstill guarantees an effective and almost lateral force-free chip flow.

SUMMARY OF THE INVENTION

The solution according to the invention is based foremost on the ideathat a thrust force is imparted to the comparatively long flowing chipsand shearing chips by the tool feed before their removal from theworkpiece, which thrust force can be used to aid chip removal undersuitable geometric conditions. In this, use is made of the recognitionthat a chip deformation, which leads to chip compression and lateralforces, must be avoided after the creation of the chips. In order toachieve this, it is proposed according to the inventive method that thechips are transported from their point of origin into an annular,axially extending chip collecting space formed between a drill shank andthe bore wall, before at least a fraction of these is separated from theworkpiece, and that at least a fraction of the chips is form-fittinglypicked up in the region between two lock or screw turns by a feed helix,one end of which is adjacent to the chip collecting space and whichprotrudes over the drill shank with a smaller diameter than the bore andco-rotates with the drilling tool, and is transported essentiallyaxially parallel out of the bore hole under friction with the bore walland gliding up on the feed helix. It may further be achieved thatfurther chips, which are entangled with the chips form-fittingly glidingup on the feed helix, are transported in packets out of the bore hole.

With respect to the device this aim can be realized in that the chipchannels have a chip guiding surface which is opposed to the chipdiverting surface on the side of the cutting insert and which is alignedessentially parallel thereto and is disposed on the adjacent segmentportion and/or that the chip diverting surfaces terminate at an axialdistance from the cutting edges at an essentially parallel alignedrearward free edge and merge thereat into a chip removal surface whichrearwardly delimits the appertaining segment portion in the direction ofthe drill shank and which ascends helically in the direction of chiptravel to the next chip channel with an angle of ascent of less than40°. The axial extent of the chip diverting surface between theeffective cutting edges and the free edge should be chosen to becomparatively short and should correspond to approximately 1.5 to 3times the diameter of the circumscribing circle of the cutting inserts.It is thus ensured that a major fraction of the flowing chips orshearing chips created in the drilling process reach the chip removalsurface before they are totally removed from the workpiece. In order tomake the transfer of the chips to the chip removal surface easier, thechip guiding surfaces should have an axial extent which is preferably1.5 to 3 times greater than that of the adjacent chip divertingsurfaces, and the chip guiding surfaces should be angled off at theirrearward end in the direction of the chip diverting surface and chipremoval surface of the adjacent segment portion.

In order to be able to modularly assemble the drilling tool matching itto the intended application, it is proposed according to a preferredembodiment of the invention that the drill head is removably connectedto the drill shank and/or that the drill shank consists of at least twoshank sections which are joined to each other at axial separationpoints, wherein the appertaining sections of the feed helix merge intoeach other without steps and/or gaps in the region of the separationpoint.

The chip channels on the side of the drill axis are expedientlydelimited in the region between the chip diverting surface and the chipguiding surface by a chip deflecting surface which broadens conicallyfrom the entrance point at the side of the cutting edge up to thediameter of the drill shank. In this, it is of importance that the chipcollecting space following the chip channels in the direction of chipflow expands with respect to the cross section of the chip channels, sothat the entering chips can be pushed largely without force into thechip collecting space.

Due to the fact that the chip guiding surfaces block the immediateworking and mounting access to the adjacent chip diverting surfaces,additional measures have to be taken which enable the production of thecutting insert seats and the mounting of the cutting inserts. Thesemeasures may, for example, consist in that the cutting inserts aredisposed in at least one exchangeable holder which is removably fixed tothe segment portions of the drill head, which holder can in turn bemounted in a corresponding recess of the segment portions. Additionallyor alternatively, the part of the segment portions which entails thechip guiding surface can be formed to be a separate filling piece whichis removably fixed to the appertaining segment portion and preferablyconsists of hard material.

The design of the drill head according to the invention makes itpossible that exit nozzles for a coolant are disposed on the face of thesegment portions in the proximity of the chip guiding surfaces, whichnozzles are directed obliquely at the cutting inserts. The drainingcoolant contributes additionally to the chip removal.

For the centering of the drill head in the bore hole it is of advantage,especially when drilling deep bores, when the drill head comprises anexchangeable centering drill which is disposed axially centered andaxially protrudes over the face of the drill head and the effectivecutting edges of the cutting inserts. The working region of the radiallyinnermost cutting insert should in any case extend to and overlap withthat of the centering drill. The centering drill may also be providedwith a coolant bore which opens essentially axially close to the drilltip.

According to a preferred embodiment of the invention, it is providedthat the feed helix has a diameter which is larger than the diameter ofthe drill shank and which is smaller than the diameter of the drillhead. The width of the feed helix should be less than one fifth,preferably less than one tenth, of its pitch which defines the width ofthe chip removal groove. The annular space, which is thus created andwhich is penetrated by the feed helix, between the drill shank and thebore wall should be dimensioned such that the chips fit through theannular space and can be form-fittingly picked up at their lock or screwturns by the feed helix rotating past. To this end, the feed helixexpediently has a smooth surface with a preferably rounded crosssection. In general, the feed helix may also have a three-edged orfour-edged cross section with rounded edges. It may, for instance, beformed to be a wire helically encompassing the cylindrical drill shank,preferably welded thereon, wherein the helically wound wire may also beplaced onto the drill shank such that it cannot slip and is fixed to thedrill shank only with its ends, preferably by means of welding.According to a further preferred embodiment of the invention, it isprovided that the feed helix is disposed on the outer surface of a pieceof pipe adapted to be removably placed onto the drill shank. This designhas the advantage that pieces of pipe with differently designed anddimensioned feed helixes may easily be substituted for one another inorder to be matched to the chip shapes created during the drillingprocess.

The drill head side end of the feed helix expediently ends at an axialdistance from the chip removal surface of the drill head, so that anaxial chip collecting space is formed, in which larger and smaller chipsmay be entangled in packets before they are picked up by the feed helix.The removal of the chips is then effected due to the friction with thebore wall essentially axially by means of the feed helix rotating past.The angles of ascent of the feed helix and of the drill head side chipremoval surface are expediently chosen to be approximately of the samemagnitude. They are preferably less than 25°.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is further described with reference tothe accompanying drawing, in which:

FIG. 1a and FIG. 1b show two side views of a drilling tool from twodirections which are rotated by 90° with respect to each other;

FIG. 2 shows a frontal face view onto the drill head of the drillingtool according to FIG. 1a and FIG. 1b;

FIG. 3 shows a side view of a drilling tool having a removable drillhead and modularly assembled shank sections.

DETAILED DESCRIPTION OF THE INVENTION

The drilling tool shown in the drawings consists essentially of a drillshank 14 provided with a feed helix 12 delimiting a helical chip removalgroove 10 and adapted to be clamped in a machine spindle (not shown) anda preferably removable drill head 16 disposed on the face of the drillshank 14. The drill head has two segment portions 20 which are delimitedradially outwardly by partially cylindrical circumferential surfaces 22and which are separated from each other by chip channels 18 which arealigned essentially axially parallel. Further, three cutting inserts 26,which are radially spaced with respect to each other and to the drillaxis, are disposed in the region of the axially parallel, radial chipdiverting surfaces 24 of the chip channels 18, the faces 28 of whichinserts 26 are, in the depicted embodiment, aligned with respect to thecorresponding chip diverting surfaces 24 and the effective cutting edges30 of which protrude over the front of the drill head 16. The cuttinginserts 26 are arranged in groups of three in an exchangeable holder 32which is disposed in a corresponding recess 34 of the drill head 16 andclamped therein by means of screws 36. The cutting edge 30 of theradially outermost cutting insert 26' radially protrudes by a smallamount over the circumference of the appertaining segment portion 20 anddefines the bore diameter D. A centering drill 38 is additionallyremovably mounted in an axially centered bore of the drill head 16,which centering drill axially protrudes with its tip over the front faceof the drill head 16 and the cutting edges 30 of the cutting inserts 26,26'.

As can be seen especially in FIG. 1a and FIG. 1b, the drill head 16 hasa larger diameter than the drill shank 14. In this way there resultsduring a drilling operation behind the drill head, an annular space 40which extends along the drill shank 14 and is penetrated by the feedhelix 12, and which is outwardly delimited by the bore wall, throughwhich annular space the chips created by the drilling operation can beremoved.

The chip channels 18 of the drill head have a chip guiding surface 42disposed on the adjacent segment portion 20, which is located on theside opposite the cutting insert and opposed to the chip divertingsurface 24 on the side of the cutting insert and aligned theretoessentially parallel, as well as a chip deflecting surface 44 arrangedbetween the chip diverting surface 24 and the chip guiding surface 42,which conically widens from the cutting edge side entrance point up tothe diameter of the drill shank 14. The chip guiding surface and thechip deflecting surface ensure that the chips cannot expand uncontrolledupon their creation, so that they can pass through the annular space 40without deformation and compression.

The chip diverting surfaces 24 end at a comparatively short distance,which corresponds approximately to 1.5 to 3 times the diameter of thecircumscribing circle of the cutting inserts, from the cutting edges atan essentially radially aligned rearward free edge 46, which isfollowed, under formation of an expanded chip collecting space 48, by achip removal surface 50 which delimits the corresponding segment portion20 rearwardly in the direction of the drill shank 14 and which ascendshelically in the direction of chip flow toward the next chip channel 18with an angle of ascent of approximately 20°. The chip guiding surfaces42 are 1.5 to 3 times greater with respect to their axial extent thanthe adjacent chip diverting surfaces 24 and are angled off at theirrearward end 52 in the direction of the chip diverting surface 24 andchip removal surface 50 of the adjacent segment portion 20. The insideedges between the chip deflecting surface 44 and the adjacent chipdiverting, guiding and removal surfaces 24, 42, 50 are rounded and formdistorted transitions for a smooth chip flow.

Exit nozzles 54 for a coolant and lubricant are disposed on the frontface of the segment portions close to the chip guiding surfaces 42,which are directed obliquely in the direction of the cutting inserts 26.Further exit points 56 for coolant and lubricant are located in thevicinity of the tip of the centering drill 38. The coolant and lubricantemerging from the exit nozzles has the purpose of not only cooling butalso to aid the chip flow through the chip channels 18 and the annularspace 40.

The removal of lock-shaped and screw-shaped chips is preferably effectedby means of the feed helix 12, though. To this end, the feed helix hasan external diameter d_(w) which is larger than the shank diameterd_(s), but is smaller than the bore diameter D (see FIG. 1a and FIG.1b). Further, the width b of the feed helix 12 is considerably smallerthan its pitch w+b which defines the width w of the chip removal groove10. The feed helix 12 can be formed onto the drill shank 14 or formed tobe a wire helically surrounding the cylindrical drill shank and beingwelded thereto. At its drill head side end 58 the feed helix 12 ends ata distance from the helical chip removal surfaces 50 of the drill headand thereby delimits the helix-less chip collecting space 48. The angleof ascent of the feed helix corresponds approximately to the angle ofascent of the helical chip removal surfaces 50 and is approximately 20°in the depicted embodiment.

The drilling tool shown in FIG. 3 differs from the drilling tool shownin FIGS. 1a and b in that drill head 16 is removably connected to thedrill shank 14 at a separation point 60 and in that the drill shank 14is composed of a number of shank sections 14', 14", 14'" which areconnected to each other at separation points 62, 64. In order to avoid achip jamming, the feed helix sections 12', 12" merge into each otherwithout steps or gaps in the region of the separation point 62. It isthereby possible to modularly assemble the drilling tool to match thework to be performed.

The drilling tool described above is advantageously used for deep holeboring of workpieces, in which comparatively long, screw- or lock-shapedflow chips are created to some extent. A fraction of the flow chips isled through the chip channels 18 into the chip collecting space 48 inthe region of the chip removal surface 50 by means of the chip guidingsurfaces and the chip deflecting surfaces 44 before they are separatedfrom the workpiece. In this, the thrust force imparted to the chip bythe forward feed of the workpiece is used to remove the chips largelywithout compression or deformation work. Smaller and larger chips areentangled in the chip collecting space 48 and are picked up in packetsby the feed helix and transported essentially axially outwards out ofthe annular space 40. In this, the feed helix form-fittingly engages theturns of the chips. The friction with the bore wall ensures that thechips glide up on the feed helix 12 and are transported out of theannular space in an essentially axially parallel direction. The flow ofcoolant and lubricant only has a supporting function in this process.

In summary the following is to be stated: The invention is related to adrilling tool for machine tools, comprising a drill shank 14 providedwith a feed helix 12 delimiting a helical chip removal groove 10 andadapted to be clamped in a machine spindle, and comprising a drill head16 disposed on the face of the drill shank 14. The drill head has twosegment portions 20 which are delimited radially outwardly by partiallycylindrical circumferential surfaces 22 which are seperated from eachother by chip channels 18 which adjoin each other in a circumferentialdirection and which are aligned essentially axially parallel, and whichdrill head has at least two cutting inserts 26 which are disposed atdifferent radial distances from the axis of the drill and which eachhave a cutting edge 30 protruding over the face of the drill head 16.The chip channels 18 are delimited on the side of the cutting inserts byan axially parallel, radial chip diverting surface 24 and by a chipguiding surface 42 which is opposed to the chip diverting surface 24 andwhich is aligned essentially parallel thereto and is disposed on theadjacent segment portion 20. The chip diverting surfaces 24 terminate atan axial distance from the cutting edges at an essentially parallelaligned rearward free edge and merge thereat into a chip removal surface50 which rearwardly delimits the appertaining segment portion 20 in thedirection of the drill shank 14 and which ascends helically in thedirection of chip travel to the next chip channel 18. The annular spacebetween the chip removal surface and the drill head side end 58 of thefeed helix 12 forms a chip collecting space 48, from which the chipscreated in the drilling process are transported outwards in packets bythe feed helix 12.

What is claimed is:
 1. A drilling tool for machine tools, comprising adrill shank provided with a feed helix delimiting a helical chip removalgroove and adapted to be clamped in a machine spindle, and comprising adrill head disposed on a face of the drill shank, said drill headincluding two segment portions delimited radially outwardly by partiallycylindrical circumferential surfaces together forming a commoncircumferential cylinder and which are separated from each other by chipchannels adjoining each other in a circumferential direction, the chipchannels being aligned essentially axially parallel, and merging in thechip removal groove in a chip flow direction, and said drill headincluding at least two cutting inserts disposed at different radialdistances from the axis of the drill head with partially overlappingworking areas in an appertaining recess of the segment portions in theregion of at least one axially parallel radial chip diverting surfacewith faces of said inserts aligned thereto, and having at least oneactive cutting edge protruding over a face of the drill head, whereinthe cutting edge of the outermost cutting insert protrudes radially overthe appertaining partially cylindrical circumferential surface and thedrill head has a larger outer diameter than the drill shank, wherein thechip channels have at least one chip guiding surface opposed to the chipdiverting surface on the side of the cutting insert and alignedessentially parallel thereto and disposed on the adjacent segmentportion.
 2. The drilling tool of claim 1, wherein the chip divertingsurfaces terminate at an axial distance from the cutting edges at anessentially parallel aligned rearward free edge and merge thereat into achip removal surface rearwardly delimiting the appertaining segmentportion in the direction of the drill shank and ascending helically inthe direction of chip travel to the next chip channel with an angle ofascent of less than 40°.
 3. A drilling tool for machine tools,comprising a drill shank provided with a feed helix delimiting a helicalchip removal groove and adapted to be clamped in a machine spindle, andcomprising a drill head disposed on a face of the drill shank, saiddrill head having two segment portions delimited radially outwardly bypartially cylindrical circumferential surfaces together forming a commoncircumferential cylinder and separated from each other by chip channelsadjoining each other in a circumferential direction, aligned essentiallyaxially parallel, and merging in the chip removal groove in a chip flowdirection, and said drill head including at least two cutting insertsdisposed at different radial distances from the axis of the drill headwith partially overlapping working areas in an appertaining recess ofthe segment portions in the region of at least one axially parallelradial chip diverting surface with faces of said inserts alignedthereto, and having at least one active cutting edge protruding over aface of the drill head, wherein the cutting edge of the outermostcutting insert protrudes radially over the appertaining partiallycylindrical circumferential surface and the drill head has a largerouter diameter than the drill shank, wherein the chip diverting surfacesterminate at an axial distance from the cutting edges at an essentiallyparallel aligned rearward free edge and merge thereat into a chipremoval surface rearwardly delimiting the appertaining segment portionin the direction of the drill shank and ascending helically in thedirection of chip travel to the next chip channel with an angle ofascent of less than 40°, and the angles of ascent of the feed helix andof the chip removal surface are approximately of the same magnitude. 4.The drilling tool of claim 1, wherein the axial extent of the chipdiverting surface between the effective cutting edges and the free edgecorresponds to 1.5 to 3 times the diameter of a circumscribing circle ofthe cutting inserts.
 5. The drilling tool of claim 1, wherein the chipguiding surfaces have an axial extent which is 1.5 to 3 times greaterthan that of the adjacent chip diverting surfaces.
 6. The drilling toolof claim 2, wherein the chip guiding surfaces are angled off at theirrearward end in the direction of the chip diverting surface and the chipremoval surface of the adjacent segment portion.
 7. The drilling tool ofclaim 1, wherein the chip channels are delimited in the region betweenthe chip diverting surface and the chip guiding surface by a chipdeflecting surface which broadens conically from an entrance point atthe side of the cutting edge up to the diameter of the drill shank. 8.The drilling tool of claim 1, wherein the cutting inserts are disposedin at least one exchangeable holder removably fixed to the segmentportions of the drill head.
 9. The drilling tool of claim 1, wherein apart of the segment portions which includes the chip guiding surface isformed as a separate filling piece removably fixed to the appertainingsegment portion and comprising a hard material.
 10. The drilling tool ofclaim 1, wherein the drill head comprises an exchangeable centeringdrill disposed axially centered and axially protruding from the face ofthe drill head and the active cutting edges of the cutting inserts. 11.The drilling tool of claim 10, wherein the working area of the radiallyinnermost cutting insert extends to and overlaps with that of thecentering drill.
 12. The drilling tool of claim 1, wherein exit nozzlesfor a coolant are disposed on the face of the segment portions in theproximity of the chip guiding surfaces, said nozzles being directedobliquely at the cutting inserts.
 13. The drilling tool of claim 10,wherein at least one coolant bore penetrates the centering drillessentially axially parallel to the axis of the drill head and opensclose to a drill tip of the centering drill.
 14. The drilling tool ofclaim 1, wherein the feed helix has a diameter larger than the diameterof the drill shank and smaller than the diameter of the drill head. 15.The drilling tool of claim 1, wherein the width of the feed helix isless than one fifth of its pitch defining the width of the chip removalgroove.
 16. The drilling tool of claim 1, wherein the feed helixincludes a smooth surface with a rounded cross section.
 17. The drillingtool of claim 1, wherein the feed helix is formed as a wire helicallyencompassing the cylindrical drill shank.
 18. The drilling tool of claim1, wherein the feed helix is formed as a helically wound wire placedonto the drill shank such that the wire cannot slip and is fixed to thedrill shank by means of welding.
 19. The drilling tool of claim 1,wherein the feed helix is disposed on an outer surface of a piece ofpipe adapted to be removably placed onto the drill shank.
 20. Thedrilling tool of claim 1, wherein the feed helix has a three-edged orfour-edged cross section.
 21. The drilling tool of claim 1, wherein adrill head side end of the feed helix ends at an axial distance from thechip removal surface of the drill head, thereby forming an axial chipcollecting space.
 22. The drilling tool of claim 1, wherein angles ofascent of the feed helix and of a chip removal surface are approximatelyof the same magnitude.
 23. The drilling tool of claim 22, wherein theangle of ascent of the feed helix is less than 25°.
 24. The drillingtool of claim 1, wherein the drill head is removably connected to thedrill shank.
 25. The drill tool of claim 1, wherein the drill shankcomprises at least two shank sections joined to each other at axialseparation points, wherein appertaining sections of the feed helix mergeinto each other without steps or gaps in the region of the separationpoints.
 26. A method for removing chips, created in a drilling operationforming a bore hole in a workpiece with a rotating drilling tool,wherein the chips are transported from their point of origin into anannular, axially extending chip collecting space formed between a drillshank and a bore wall in the workpiece, before at least a fraction ofthe chips are separated from the workpiece, and that at least a fractionof the chips is form-fittingly picked up in the region between two lockor screw turns by a feed helix, one end of which is adjacent to the chipcollecting space and which protrudes over the drill shank with a smallerdiameter than the bore hole and co-rotates with the drilling tool, andthe chips are transported essentially axially parallel out of the borehole under friction with the bore wall and gliding up on the feed helix.27. The method of claim 26, wherein further chips, which are entangledwith the chips form-fittingly gliding up on the feed helix, aretransported in packets out of the bore hole.